In an internal combustion engine, a plurality of pistons reciprocate inside of a plurality of respective cylinders. It is desirable to reduce the friction between the piston, and particularly the skirt of the piston, and the cylinder walls. Such a decrease in the friction results in greater efficiency of the engine.
Currently, piston skirts have finished surfaces which are defined by smooth curved raised portions and intermediate valley portions. This design resembles a sine wave configuration in that is has smooth alternating curved raised and smooth curved valley portions.
To further decrease friction between the skirt portion piston and the cylinder walls, it is known to coat the skirt portion with a fluorocarbon polymer. For example, U.S. Pat. No. 2,817,562 to Fleming et al, issued Dec. 24, 1957 shows a piston assembly having a skirt portion coated with a thin coating of polytetrafluoroethylene.
Also, the use of lightweight materials, such as aluminum to comprise the piston increases the efficiency of the engine. Such an aluminum piston is shown in U.S. Pat. No. 4,338,858 to Reitz, issued July 13, 1982.